using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace teardrop
{
    class Crypto
    {
        // This is used to generate a random string. Can be used to generate the encryption key
        private static Random random = new Random();
        public static string GetRandomString(int length)
        {
            const string chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
            return new string(Enumerable.Repeat(chars, length)
              .Select(s => s[random.Next(s.Length)]).ToArray());
        }

        // This code can be used to delete the encryption key from memory!
        [DllImport("KERNEL32.DLL", EntryPoint = "RtlZeroMemory")]
        public static extern bool ZeroMemory(IntPtr Destination, int Length);

        // This will generate a salt for the encryption process
        public static byte[] GenerateRandomSalt()
        {
            byte[] data = new byte[32];

            using (RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider())
            {
                for (int i = 0; i < 10; i++)
                {
                    rng.GetBytes(data);
                }
            }

            return data;
        }

        // This will encrypt a file with a random sault.
        public static void FileEncrypt(string inputFile, string password)
        {
            byte[] salt = GenerateRandomSalt();

            FileStream fsCrypt = new FileStream(inputFile + Properties.Settings.Default.extension, FileMode.Create);

            byte[] passwordBytes = System.Text.Encoding.UTF8.GetBytes(password);

            RijndaelManaged AES = new RijndaelManaged();
            AES.KeySize = 256;
            AES.BlockSize = 128;
            AES.Padding = PaddingMode.PKCS7;

            var key = new Rfc2898DeriveBytes(passwordBytes, salt, 50000);
            AES.Key = key.GetBytes(AES.KeySize / 8);
            AES.IV = key.GetBytes(AES.BlockSize / 8);

            AES.Mode = CipherMode.CFB;

            fsCrypt.Write(salt, 0, salt.Length);

            CryptoStream cs = new CryptoStream(fsCrypt, AES.CreateEncryptor(), CryptoStreamMode.Write);

            FileStream fsIn = new FileStream(inputFile, FileMode.Open);

            byte[] buffer = new byte[1048576];
            int read;

            try
            {
                while ((read = fsIn.Read(buffer, 0, buffer.Length)) > 0)
                {
                    Application.DoEvents();
                    cs.Write(buffer, 0, read);
                }

                fsIn.Close();
            }
            catch (Exception ex)
            {
                Console.WriteLine("Error: " + ex.Message);
            }
            finally
            {
                cs.Close();
                fsCrypt.Close();
            }
        }

        // This will decrypt a file
        public static void FileDecrypt(string inputFile, string outputFile, string password)
        {
            byte[] passwordBytes = System.Text.Encoding.UTF8.GetBytes(password);
            byte[] salt = new byte[32];

            FileStream fsCrypt = new FileStream(inputFile, FileMode.Open);
            fsCrypt.Read(salt, 0, salt.Length);

            RijndaelManaged AES = new RijndaelManaged();
            AES.KeySize = 256;
            AES.BlockSize = 128;
            var key = new Rfc2898DeriveBytes(passwordBytes, salt, 50000);
            AES.Key = key.GetBytes(AES.KeySize / 8);
            AES.IV = key.GetBytes(AES.BlockSize / 8);
            AES.Padding = PaddingMode.PKCS7;
            AES.Mode = CipherMode.CFB;

            CryptoStream cs = new CryptoStream(fsCrypt, AES.CreateDecryptor(), CryptoStreamMode.Read);

            FileStream fsOut = new FileStream(outputFile, FileMode.Create);

            int read;
            byte[] buffer = new byte[1048576];

            try
            {
                while ((read = cs.Read(buffer, 0, buffer.Length)) > 0)
                {
                    Application.DoEvents();
                    fsOut.Write(buffer, 0, read);
                }

                
            }
            catch (CryptographicException ex_CryptographicException)
            {
                Console.WriteLine("CryptographicException error: " + ex_CryptographicException.Message);
            }
            catch (Exception ex)
            {
                Console.WriteLine("Error: " + ex.Message);
            }

            try
            {
                cs.Close();
            }
            catch (Exception ex)
            {
                Console.WriteLine("Error by closing CryptoStream: " + ex.Message);
            }
            finally
            {
                fsOut.Close();
                fsCrypt.Close();
            }

        }
    }
}
